This application claims priority from Australian Provisional Application 2010901452 filed 7 Apr. 2010, which is hereby incorporated by reference.
Schemes for the transmission and storage of video material typically utilize compression schemes to reduce the storage and bandwidth requirements associated with the video material. One class of compression schemes makes use of the redundancy between successive frames of a video sequence. In these schemes, successive frames are represented in terms of a transformation of a reference frame. For example, in block motion prediction schemes, each frame is divided into a plurality of fixed size blocks. A frame to be transmitted is first coded in terms of the blocks of a reference frame by finding the block in the reference frame which matches the corresponding block in the frame to be coded. The coded frame can then be initially approximated by a list of vectors that specify the movement of a block in the reference frame to the corresponding block of the frame to be coded. The difference between this approximation and the actual frame is then coded using an appropriate compression algorithm. Since the difference between the approximation frame and the actual frame contains much less information than the actual frame, a significant savings in the number of bits needed to represent the new frame is obtained.
The amount of memory needed to store the reference frame is a significant problem, particularly in high definition video transmissions for small handheld devices. Small handheld devices typically rely on system-on-chip designs that have insufficient memory to hold a reference frame of a high-definition transmission. As a result, a separate memory chip or chips are required. These additional chips increase the cost of the device, and in addition, use substantial additional power. The additional power is particularly problematic in battery-operated devices.
One possible solution to the memory problem would be to use a compression algorithm to store the reference frame in its memory. When pixels of the reference frame are needed by the compression engine, the compressed reference frame would be partially decompressed to provide the pixels to the compression engine. If a lossless compression scheme is used for storing the reference frame, the memory savings are insufficient to avoid the need for additional memory in a handheld device such as those discussed above.
If a lossy compression scheme is used for storing the reference frame, the reference frame used by the transmitter will be different than the reference frame used by the receiver. This leads to artifacts in the video sequence generated by the receiver. These artifacts are particularly troublesome in compression schemes in which each frame utilizes the previous frame as its “reference” frame. In such systems, the artifacts become more pronounced with each frame.